为设备安装比最新版本更低的 IOS 版本
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/12635862/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Installing a lower IOS version than the latest one to a device
提问by Ilker Baltaci
I know that it is possible to install lower versions of IOS to jailbroken devices over various tools by creating custom firmware.The problem is we have some test devices in the company and we want to have one device eactly with IOS 4.3. It will not be downgrade since the device itself has IOs 4.2.1 installed.Is there a documented way to active it and the most importantly where can i find older IOS versions?
我知道可以通过创建自定义固件，通过各种工具将较低版本的 IOS 安装到越狱设备上。问题是我们公司有一些测试设备，我们希望有一台设备与 IOS 4.3 完全一致。它不会降级，因为设备本身安装了 IOs 4.2.1。是否有记录的方法来激活它，最重要的是在哪里可以找到旧的 IOS 版本？
采纳答案by Bastian
Apple doesn't want you to install anything but the latest version available of iOS, so every install of a firmware will get checked with Apple's servers.
除了最新版本的 iOS 之外，Apple 不希望您安装任何东西，因此每次安装固件都会通过 Apple 的服务器进行检查。
There is a way to save the authorization for other firmwares with tools like TinyUmbrella, but you can only save the authorization of the currently allowed version; so, if you did not use TinyUmbrella 2 years ago when iOS 4 was the newest version, there is no way to downgrade your device.
使用TinyUmbrella等工具可以保存其他固件的授权，但只能保存当前允许版本的授权；因此，如果您在 2 年前 iOS 4 是最新版本时没有使用 TinyUmbrella，则无法降级您的设备。
回答by jcesarmobile
EDIT: Editing because this no longer works and it gets downvoted by people who didn't read the comments.
编辑：编辑，因为这不再有效，并且被没有阅读评论的人拒绝。
Apple wants us to use the latest version, and develop for the latest version, there is no way of downgrading anymore.
苹果要我们用最新版本，开发最新版本，没有降级的办法了。
OLD ANSWER: You can download any firmware for any iOS device here
旧答案：您可以在此处为任何 iOS 设备下载任何固件
To install it, you have to go to iTunes and click on update with the altkey pressed, then you can choose the .ipswfile with the firmware you want.
要安装它，您必须转到 iTunes 并在按下alt键的情况下单击更新，然后您可以选择.ipsw包含所需固件的文件。
For the "This device isn't elegible..." message try this
对于“此设备不可读......”消息试试这个
